British Standard Pipe

The British Standard Pipe (BSP) is a family of standard screw thread types that has been adopted internationally for interconnecting and sealing pipe ends by mating an external (male) with an internal (female) thread and has been adopted as a standard scale used in plumbing fittings, except in the United States where NPT is the standard used.

Types

Two types of threads are distinguished:

• Parallel (straight) threads, British Standard Pipe Parallel thread (BSPP; originally also known as^[1] British Standard Pipe Fitting thread/BSPF and British Standard Pipe Mechanical thread/BSPM), which have a constant diameter; denoted by the letter G.
• Taper threads, British Standard Pipe Taper thread (BSPT), whose diameter increases or decreases along the length of the thread; denoted by the letter R.

BSPT Pipe Threads.^[2]

These can be combined into two types of joints:

Jointing threads

These are pipe threads where pressure-tightness is made through the mating of two threads together. They always use a taper male thread, but can have either parallel or taper female threads. (International standards require all female threads to be parallel.)

Longscrew threads

These are parallel pipe threads used where a pressure-tight joint is achieved by the compression of a soft material (such as an o-ring seal or a washer) between the end face of the male thread and a socket or nipple face, with the tightening of a backnut.

Thread form

The thread form follows the British Standard Whitworth standard:

• Symmetrical V-thread in which the angle between the flanks is 55° (measured in an axial plane)
• One-sixth of this sharp V is truncated at the top and the bottom
• The threads are rounded equally at crests and roots by circular arcs ending tangentially with the flanks where r=0.1373P
• The theoretical depth of the thread is therefore 0.6403 times the nominal pitch

Pipe thread sizes

A list of 16 thread sizes are defined by the standards, ranging from ¹⁄₁₆ to 6. The size number was originally based on the inner diameter (measured in inches) of a steel tube for which the thread was intended, but contemporary pipes tend to use thinner walls to save material, and thus have an inner diameter larger than this nominal size. In the modern standard metric version, it is simply a size number, where listed diameter size is the major outer diameter of the external thread. For a taper thread, it is the diameter at the "gauge length" from the small end of the thread. The taper is 1 to 16, meaning that for each 16 units of measurement increase in the distance from the end, the diameter increases by 1 unit of measurement.

Nominal size	Dash size	Thread density	Thread pitch		Major diameter		Minor diameter[3][4]		Gauge length		Typ. nut size	Corresponding pipe				Tapping drill size
												DN	OD		Thickness	BSP.PL, Rp	BSP.F, G
(in)		(in^−1)	(mm)	(in)	(mm)	(in)	(mm)	(in)	(mm)		(mm)	(mm)	(mm)	(in)	(mm)	(mm)	(mm)
^1⁄16	−1	28	0.907	0.0357	7.723	0.304	6.561	0.2583	4±0.9							6.60	6.80
^1⁄8	−2	28	0.907	0.0357	9.728	0.383	8.565	0.3372	4±0.9		15	6	10.2	0.40	2	8.60	8.80
^1⁄4	−4	19	1.337	0.0526	13.157	0.518	11.445	0.4506	6±1.3		19	8	13.5	0.53	2.3	11.50	11.80
^3⁄8	−6	19	1.337	0.0526	16.662	0.656	14.950	0.5886	6.4±1.3		22 or 23	10	17.2	0.68	2.3	15.00	15.25
^1⁄2	−8	14	1.814	0.0714	20.955	0.825	18.633	0.7336	8.2±1.8		27	15	21.3	0.84	2.6	18.75	19.00
^5⁄8	−10	14	1.814	0.0714	22.911	0.902	20.589	0.8106				16			2.6	-	21.00
^3⁄4	−12	14	1.814	0.0714	26.441	1.041	24.120	0.9496	9.5±1.8		32	20	26.9	1.06	2.6	24.25	24.50
1	−16	11	2.309	0.0909	33.249	1.309	30.292	1.1926	10.4±2.3		43	25	33.7	1.33	3.2	30.40	30.75
1 ^1⁄4	−20	11	2.309	0.0909	41.910	1.650	38.953	1.5336	12.7±2.3		53	32	42.4	1.67	3.2	39.00	39.50
1 ^1⁄2	−24	11	2.309	0.0909	47.803	1.882	44.846	1.7656	12.7±2.3		57	40	48.3	1.90	3.2	45.00	45.00
2	−32	11	2.309	0.0909	59.614	2.347	56.657	2.2306	15.9±2.3		70	50	60.3	2.37	3.6	56.75	57.00
2 ^1⁄2	−40	11	2.309	0.0909	75.184	2.960	72.227	2.8436	17.5±3.5			65	76.1	3.00	3.6
3	−48	11	2.309	0.0909	87.884	3.460	84.927	3.3436	20.6±3.5			80	88.9	3.50	4
4	−64	11	2.309	0.0909	113.030	4.450	110.073	4.3336	25.5±3.5			100	114.3	4.50	4.5
5	−80	11	2.309	0.0909	138.430	5.450	135.472	5.3335	28.6±3.5			125	139.7	5.50	5
6	−96	11	2.309	0.0909	163.830	6.450	160.872	6.3335	28.6±3.5			150	165.1	6.50	5

These standard pipe threads are formally referred to by the following sequence of blocks:

• the words, Pipe thread,
• the document number of the standard (e.g., ISO 7 or EN 10226)
• the symbol for the pipe thread type:
  • G, external and internal parallel (ISO 228)
  • R, external taper (ISO 7)
  • Rp, internal parallel (ISO 7/1)
  • Rc, internal taper (ISO 7)
  • Rs, external parallel
• the thread size

Threads are normally right-hand. For left-hand threads, the letters, LH, are appended.

Example: Pipe thread EN 10226 Rp 2½

The terminology for the use of G and R originated from Germany (G for gas, as it was originally designed for use on gas pipes; R for rohr, meaning pipe.)

ISO 228

The standard ISO 228 - Pipe threads where pressure-tight joints are not made on the threads consists of the following parts:

• ISO 228-1:2000 Dimensions, tolerances and designation
• ISO 228-2:1987 Verification by means of limit gauges

See also

AN thread British standard brass thread British Standard Whitworth Garden hose thread

National pipe thread Panzergewinde Thread angle Threaded pipe

References

1. "BSPM = British Standard Pipe Mechanical". Retrieved 19 November 2014.
2. http://www.colder.com/Portals/0/Library/Resources/Literature/WhitePapers/Documents/NPT_whitepaper.pdf
3. maryland metrics. "Maryland Metrics thread data charts". Retrieved 19 November 2014.
4. "RoyMech: Pipe Threads". Retrieved 19 November 2014.

External links

• Newman Tools Inc. and J.W. WINCO, INC. show the Whitworth form BSP or ISO pipe thread.